In order to accommodate and increase the recording density of a magnetic disk drive device, it is important that flying height (or, equivalently magnetic spacing), that is defined as the spacing between a magnetic head mounted in a magnetic head slider and a rotating magnetic disk, is narrowed. An ideal magnetic head slider has a uniform and minimal flying height over the entire surface of the magnetic disk during operation. However, the flying height of a typical slider may have fluctuations caused by the variation of manufacturing tolerance, seek operations and ambient pressure change, such as a drop in atmospheric pressure when operating at a high altitude. Accordingly, some of the magnetic head sliders, referred to as high fliers, may have relatively larger flying heights than an intended average value.
To reduce the flying height of a high flier during operation and thereby to improve the quality of data communication between the magnetic disk and slider, a Thermal Flight Control (TFC) technique (or equivalently, Write Protrusion Control technique) may be used. The TFC technique controls the flying height by use of heat energy generated by heat generating element (or, equivalently, heat source) located adjacent to the writing or recording head. Typically, the heat generating element produces a protrusion throw with a large footprint, about 50 to 200 μm in diameter, wherein the protrusion throw refers to the deformation of the magnetic head slider surface due to the heat energy. The height of a typical protrusion throw ranges from 1 to 8 nanometers. When the heat generating element is activated, the protrusion throw decreases the magnetic spacing. However, the same protrusion interacts with the air flow beneath the slider surface and increases the magnetic spacing such that the reduction in magnetic spacing generated by the protrusion is diminished. This phenomenon is known as protrusion compensation effect and decreases the efficacy of the TFC technique. In general, low write protrusion compensation is desirable in terms of power consumption of the heat generating element.
A technical challenge to overcome in a typical low compensation design is the undesirable increase in flying height sigma, which is the standard deviation of a flying height distribution, particularly when the magnetic head slider flies at high pitch angles. In general, a large flying height sigma tends to offset the gains in magnetic spacing realized by the TFC technique. As the altitude sensitivity and flying height profile degradation of the slider are associated with the protrusion compensation as well as the flying height sigma, there is a strong need for a technique that can reduce the protrusion compensation effect without significantly increasing the flying height sigma.